Process for preparing aggregates

ABSTRACT

1. A PROCESS FOR PREPARING AGGREGATES COMPRISING 8A) PREPARING A SLURRY, SAID SLURRY COMPRISING A SUSPENDING LIQUID AND DISTINCT PARTICLES OF A FIRST SOLID SUSPENDED IN SAID LIQUID, (B) PREPARING A PARTICLE BED CONSISTING OF PARTICLES OF A SECOND SOLID, (C) FORMING DROPLETS OF SAID SLURRY, AND (D) DROPPING SAID DROPLETS OF SAID SLURRY INTO SAID PARTICLE BED UNDER CONDITIONS WHERE SAID SUSPENDING LIQUID IS AT LAST PARTIALLY REMOVED FROM THE SLURRY DROPLET TO FORM AN AGGREGATE OF SAID DISTINCT PARTICLES OF SAID FIRST SOLID.

NOV.- 12, 1974 CA-LLAHAN ETAL 3,848,033

PROCESS FOR PREPARING AGGREGATES Q Filed July 13, 1972 POWDER RECYCLEUnited States Patent 3,848,033 PROCESS FOR PREPARING AGGREGATES James L.Callahan, Bedford Heights, Arthur F. Miller, Cleveland, and Wilfrid G.Shaw, Lyndhurst, Ohio, assignors to The Standard Oil Company, Cleveland,

hlO

Filed July 13, 1972, Ser. No. 271,387 Int. Cl. B29d 23/00 US. Cl. 264-139 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Moltensolutions have been frozen by dropping a melt into a bed of smallparticles, see for example US. 3,070,837; US. 3,255,036; and US.2,938,233. Such solidification has been carried out with the purpose ofcoating the pellet formed with the particles in the bed or theincorporation of large quantities of particles of the bed into the finalpellet. All these techniques of the art require that the materialsolidified be molten.

. Agglomeration of distinct particles of a solid into an aggregate hasbeen accomplished by many methods. Most common is compaction of thesolid and a binder to form a tablet. The present invention preparesaggregates which are as good as or better than those of conventionaltableting operations by a totally different method.

SUMMARY OF THE INVENTION I It has now been discovered according to thepresent invention that aggregates are easily formed by: (a) preparing aslurry, theslurry consisting of at least a suspending liquid anddistinct particles of a first solid suspended in said liquid; (b)preparing a particle bed consisting of particles of a second solid; (c)forming droplets of the slurry; and (d) dropping the droplets of theslurry into the particle bed under conditions where the suspendingliquid is at least partially removed from the slurry droplet to form anaggregate of the distinct particles of the first solid. Using theprocess of the present invention, rounded aggregates are formed whichare highly attrition resistant. Moreover, in certain applications, thepresent invention is capable of producing a rounded aggregate having avoid center. Those aggregates having a void center and single cavity inthe external surface communicating to the void center have been namedamphora. These amphora vary in relation to the shape of the aggregate,but a typical cross-sectional view of an amphora is shown in FIG. 1.These amphora are especially desirable for catalysts because the exposedouter surface of the aggregate is substantially increased as compared tothe surface of a pellet prepared by normal compaction techniques.

Slurry The important aspect of the present invention is the use of aslurry to prepare aggregates. This slurry may vary widely incomposition. The slurry consists of at least two components: (1) asuspending liquid; and (2) distinct particles of a suspended solid.

The suspending liquid may be essentially any liquid which will suspendthe solid. These liquids, of course, vary widely in nature. Some of theliquids are capable of dis- 3,848,033 Patented Nov. 12, 1974 solvinglarge quantities of the solid; whereas, others dissolve little or nosolid. Although some liquids are more compatible with the techniques ofthe present invention, any suspending liquid can be used so long as itcan be at least partially removed from the slurry droplet in the processof the invention.

The suspending liquid is removed from the slurry droplet by two basicmechanisms. The first mechanism is that of evaporation of the suspendingliquid. This liquid removal mechanism, of course, is directly related tothe vapor pressure of the suspending liquid under the conditions of thecontact of the slurry droplet with the particle bed.

The second mechanism of removing the suspending liquid from the slurrydroplet is that of the capillary action of the particle bed into whichthe droplet is dropped. Of course, the viability of the capillary actionis dependent upon a large number of factors, such as the relationshipbetween the suspending liquid and the particle bed, the porosity of theparticle bed and the temperature of the slurry drop. These factors willbe considered in greater detail in the discussion of the particle bedand the process of the invention.

In this discussion of the suspending liquid, the most importantattribute of the suspending liquid is its vapor pressure when theprimary liquid removal mechanism is evaporation. If evaporation is themain mechanism of liquid removal, the suspending liquid is normally onewhich has a relatively high vapor pressure. On the other hand, ifcapillary action is the primary mechanism, the vapor pressure of thesuspending liquid is relatively unimportant.

Liquids suitable for use as the suspending liquid in thepresentinvention include: water; alcohols, such as methanol, ethanol, butanoland hexanol; ethers, such as methyl ether, ethyl ether and the like;ketones, such as acetone, methyl ethyl ketone, methyl i-butyl ketone andthe like; esters, such as methyl acetate, butyl propionate and the like;hydrocarbons, such as hexane, cyclohexane, kerosine and the like;chlorinated hydrocarbons, such as methylene chloride,1,1,1-trichloroethane, perchloroethylene and the like; aromaticcompounds, such as benzene, toluene, chlorobenzene and the like; and anyother liquid that is capable of suspending the solid in the slurry. Thesuspending liquid may be any of these materials individually or anycombination or emulsion of liquids.

Normally, less preferred are the liquids having a very low or a veryhigh vapor pressure. These liquids, however, can be employed so long asthe liquid can be removed by the interaction of the slurry With theparticle bed.

Preferred in the present invention is the use of Water as the suspendingliquid. This liquid is inexpensive and conveniently removed from theslurry droplet by a number of techniques.

The second component of the slurry is the solid which is suspended inthe suspending liquid. For purposes of clarity, this solid is referredto as the first solid. This is the solid that is formed by the processof the present invention into at least part of the aggregate.Accordingly, the description must be rather broad, for it incorporatesany material that is agglomerated into an aggregate by the process ofthe invention.

The first solid may vary widely in composition. It may be a singlematerial, or it may be a combination of two or more solids. The solidmaterial may have many functions in the final aggregate. For example,the solid material may be the active ingredient of the final product, itcould be the binder; it could be a porosity improver; it could be anextender; it could be a surfactant; or it could serve any otherfunction.

Any of these solids may be soluble to almost any extent in thesuspending liquid, but the total combination of solids and liquid mustbe a slurry. Preferred slurries contain at least about 5 percent byweight of insoluble solids based on the weight of the suspending liquidunder the conditions of droplet formation, with slurries containing atleast about percent by weight of insoluble solids being especiallypreferred. In any particular application, however, the preferred weightof insoluble solids is highly dependent upon the solid agglomerated andthe suspend ing liquid employed in the invention.

The insoluble solids content of a given slurry may be easily determinedby forming the slurry with a measured amount of suspending liquid,bringing the slurry to the conditions of droplet formation, allowing theslurry to stand so that the undissolved solids separate from the liquidand decanting and drying the solids in the slurry. Alternatively, theslurry can be centrifuged, a measured amount of a flocculant could beadded or the slurry could be filtered to determine the insoluble solidscontent. The total solids content of the slurry, of course, is the sumof the soluble and insoluble solids of the slurry.

As noted, there is essentially no limit on the type of materials thatmay be formed into aggregates by the process of the invention. The onlycriterion that must be met is that there is a liquid in which the solidcan be slurried under the conditions of droplet formation.

Broad representative examples of the solids that may be employed in thepresent invention include: catalyst materials and catalyst precursors;clay; agricultural chemicals, such as urea, ammonium nitrate, herbicidesand insecticides; polymers, such as polyethylene, polypropylene,polystyrene, polymethylmethacrylate, and high-nitrile resins; and othermaterials such as acids, bases, polyurethane intermediates, detergents,metals, metal oxides, metal organic compounds, metal salts, solidorganic compounds, pharmaceutical chemicals, food products,carbohydrates and the like. Any of these solids could be used in theprocess of the invention.

The slurry of the invention may contain other components which arespecifically designed to enhance the desirability of the aggregateformed. These components may be dissolved or suspended in the suspendingliquid to serve various functions. For example, materials may besuitably included in the slurry as binders, porosity improvers,extenders and the like.

Many of the suspended solids in the slurry can be processed by thepresent invention to prepare a desirable hard, rounded aggregate.Others, while forming an aggregate, may not possess the desiredattrition resistance. Binders can be incorporated into the slurry torectify this problem. Suitable binders include hydrous oxide gels, suchas silica gels and alumina gel, and adhesives such as natural andsynthetic resins including rosin, pitch, polyvinyl acetate,phenol-formaldehyde resins and the like. Essentially, any material thatincreases the cohesiveness of the resulting aggregate may be used.

Porosity improvers can also be added to the slurry. Such porosityimprovers are normally materials that are initially incorporated intothe structure of the aggregate and then after the aggregate is formed,these improvers are removed by some appropriate technique. For example,a very high boiling liquid which is not removed in the process of theinvention may be incorporated into the slurry. When the aggregate isformed, this liquid is entrapped in the solid. The liquid is thenremoved by calcining the aggregate at a high temperature. The escape ofthe vapors of the high boiling liquid creates a particle having greaterporosity. As a second example, a combustible or decomposable substancecan be incorporated into the slurry. Again these particles are entrappedin the aggregate. Their removal by combustion or decomposition gives anaggregate of greater porosity.

A third desired modification of the slurry is the use of extenders. Thisis the incorporation of materials into the slurry which do notsignificantly affect the activity of the product in its intended use.For example, when aggregates of an active herbicide are made by theprocess of the present invention, inert ingredients could be added toprotect the desired plants from damage that would result if only thepure herbicide formed the aggregate. Thus, the activity of the herbicideis diluted to an appropriate con: centration.

Of course, these are only some of the examples of components of theslurry which are added'for a designed purpose. Other ingredients couldbe added to accomplish other results. For example, a combination of twononinterfering catalytic ingredients could be produced in a singleaggregate. These aggregates could be placed in a catalytic reactor, andthe reactor could be alternately or concurrently used for two differentreactions without changing the catalyst charge.

A preferred application of the invention is its use to prepare catalystaggregates from active catalyst components or catalyst precursors. Thepresent invention can be used to prepare a strong, attrition-resistantaggregate which is very suitable for fixed-bed catalytic reactions.These aggregates are conveniently made without the complex extrusion ortableting equipment normally required in pelleting operations.

One important application of the invention is the use of the process toprepare catalysts used in oxidation, ammoxidation or oxidativedehydrogenation reactions. Of special significance among these catalystsare those which contain at least the compounds of bismuth and compoundsof molybdenum. Thus, in one embodiment of the process of the presentinvention, the first solid is preferably one which contains at leastbismuth and molybdenum. Also preferred because of the desirablecatalysts prepared are the catalysts which contain at least iron,bismuth and molybdenum. Thus, in this embodiment, the first solid ispreferably one which contains at least the compounds of these threemetals.

Even though the nature of the solid suspended is not critical, the sizeof the suspended solid in the slurry is important. The suspended solidmust be of such a size that droplets of the appropriate size may beformed. Of course, this means that the size of the particle permissiblein the slurry is a direct function of the size of the droplet to beformed. If the size of the droplet is small, the particles of solid inthe slurry must be small enough to accommodate the droplet. With largerdroplets, larger particles of the suspended solid can be tolerated.

In the present invention, the best results are normally obtained byusing a suspended solid in the slurry with a particle size of less thanabout a millimeter, with those having a particle size of less than about0.2 millimeter being of special interest because of the desirableaggregate formed. The significant advantage of smaller particles is thatthe resulting aggregate tends to be more cohesive.

In the slurry, the suspended particles are discrete entities. They arespatially separated throughout the slurry by the suspending liquid. Inthe process of the invention, these separate and distinct particles areagglomerated into an aggregate without the use of compaction techniquesassociated with tableting operations. I

The concentration and density of this slurry may vary Widely. It may beextremely concentrated having a high solids concentration, or it may berather dilute. In either instance, the present invention can be appliedto produce aggregates from the slurry. In the preferred practice of thepresent invention, the slurry of the invention has a high solidscontent. This high solids concentration reduces the liquid removal loadon the particle bed into which the slurry is dropped.

One of the most important variables with respect to the shape of theaggregate obtained is the apparent viscosity of the slurry. As a broadrule, it'has been discovered in our experiments that as the apparentviscosity of the slurry is increased, the spherical nature of theaggregate formed is increased. In the practice of the invention, it hasbeen found that the preferred range of apparent viscosities is about 400to about 15,000 centipoise. Of course, this preferred range ofviscosities may vary as different solids and suspending liquids areemployed.

In the practice of the invention using water as a suspending agent, theslurry normally has a specific gravity of about 1.1 to about 3. Forslurries using other suspending liquids, these figures can beextrapolated to give a figure which should be the characteristicspecific gravity for other slurries.

Particle Bed In addition to the slurry, the present invention utilizes aparticle bed. This particle bed is composed of particles of a secondsolid which may be chemically the same or different from the firstsolid. The particle bed may vary widely in terms of composition andparticle size.

The particle bed may be composed of particles of anychemical'composition. Normally, the particles of the particle bed arenot substantially incorporated into or permanently deposited on theaggregates formed. Thus, inexpensive, inert materials, such as sand,clay, alumina, carbon, sugar, diatomaceous earth and the like, can beemployed as the compositions for the particle bed. In a preferredpractice of the invention, however, the solid of the slurry is similarin chemical composition to the solid of the particle bed. In thedescription of the invention, this means that the first solid and thesecond solid are chemically similar. I

Although the particle bed may be composed of particles of any chemicalcomposition, the nature of the particles plays a significant role in theremoval of the suspending liquid. The nature of the particles is centralwhen the suspending liquid is removed from the slurry by means ofcapillary action as described above.

In this capillary action, the droplet dropped into the particle bedinteracts with the particle bed in such a manner that the suspendingliquid is drawn out of the droplet. It has been noted that thiscapillary action is improved whenparticles having an increased porosityare employed. Accordingly, as the porosity of the solid in the particlebed is increased, the capillary action as a general rule increases. Forexample, in parallel experiments, using a particle bed of small glassbeads'which have a very, low porosity and a second particle bedof aporous carbon, the capillary action noted (i.e. the rate of'liquidremoval and attendant rigidification) with the carbon particle 'bed issubstantially greater than the glass-bead particle bed. Thus, if liquidremoval by means ofcapillary action is contemplated, care should betaken to assure that the particle bed contains a solidof the desiredporosity. I

" A second important aspect of the nature of the second solid which isused to make the particle bed is its relationship with the slurry. Theparticle bed may be repulsed or attracted to the slurry. For example, anaqueous slurry dropped into a hydrophobic particle bed would be repulsedby the bed and would produce a significantly'different shaped aggregatethan would be produced by a neutral or a hydrophilic particle bed. Thus,the interaction between the particle bed and the slurry droplets can bevaried to vary the shape of the aggregate formed.

The basic feature of the particle bed is its ability to accept and atleast partially encompass the droplets of the slurry without completelydestroying the shape of the droplet. To illustrate this phenomenon,consider the dropping of a. droplet of slurry on a flat, solid surface.The

'droplet shape is completely distorted upon impact with particles in thebed has a significant impact on the shape of the droplet. Broadly, thesize permissible is dependent upon a number of factors of thepreparation, such as the composition of the slurry, the apparentviscosity of the slurry, the nature of the particles in the particlebed, the temperature of the bed and the desired shape of the finalaggregate. The parameters on these factors can be altered until theappropriate aggregate is obtained. Generally, as smaller particles areused in the particle bed, the aggregates formed have more of a sphericalshape. Also, as the density or apparent viscosity of the slurry isincreased, the effect of the size of the particle on the fina aggregateis reduced.

In the preferred practice of the present invention, it has been observedthat the size of the particles in the particle bed is preferablymaintained below about 500 microns, with sizes between about 1 and about200 microns being preferred.

The density of the particle bed at the time of the impact of the slurrydroplet also has a significant effect on the shape of the aggregateformed in the process of the present invention. A lower density particlebed creates less impact of the droplets on the bed, and thus, thedistortion of the droplet shape is reduced. The lower density is readilyobtained by using a low density solid or by fluffing or fiuidizing ahigher density solid. Fluidizing a solid has an additional benefit inthat the heat transfer characteristics of the particle bed are improved.Thus, the removal of the suspending liquid from the slurry is normallyenhanced by using 'a fluidized particle bed even though other changesoccur.

Process of Invention of the broad concept of the present invention. Thepreparation of amphora, however, utilizes special techniques of thepresent invention.

The droplets of slurry can be formed by a number of known techniques.Devices as simple as a medicine dropper areconveniently used to preparesuitable aggregates. Of course, in a commercial operation, a deviceforming a plurality of droplets at one time would normally be necessary.

The size of the aggregates formed is directly proportional to the sizeof the droplet. As the size' of the slurry droplet is increased, thesize of the aggregate is increased. Using essentially uniform dropletsunder a given set of operating conditions, yields of substantiallyuniform aggregate are obtained.

The slurry droplets are usually introduced to the particle bed by meansof a gravity drop to an essentially perpendicular particle bed. Thedroplets, however, may be introduced to the particle bed by othertechniques, such as propelling the slurry droplets or dropping thedroplets in a strong countercurrent flow of gas. These and other methodsof dropping the slurry can be used to increase or decrease the impact ofthe slurry droplet on the particle bed. For example, the particle bedcould have a reciprocating motion with respect to the source of theslurry droplets. When the slurry droplet impacts on the particle bed asthe particle bed is moving away from the droplet source, the force ofthe impact of the droplet on the bed is reduced.'0n the other hand, ifthe particle bed is moving toward the droplet source, the force of theimpact is increased.

In the present invention, the path of the droplets need not beperpendicular to the bed. The droplets can be dropped on the particlebed at any angle or even propelled across the surface of the particlebed. Any of these techniques could be employed and are encompassed bythe term dropping" as used herein.

Of course, in the practice of the process of the invention, the natureof the slurry and the nature of the parti- 7 cle bed play a preeminentrole in the shape of the aggregate formed. Yet, other factors, such asdrop height, movement of the bed after droplet impactand temperature,also play important roles.

The drop height may vary widely andis dependent largely upon the shapeof aggregate desired. With a short drop height, a thick slurry and alow-density, finely-divided particle bed, an almost perfectly sphericalaggregate can be obtained. Generally, as the dropiheight is increased,the distortion from a spherical shape .is more pronounced. The dropheight may vary from as small as a fraction of an inch to a height ofseveral feet or more. Movement of the particle bed may be desirable. Onebasic goal in imparting movement to the particle bed is to continuouslyexpose fresh solid of the particle bed to the slurry droplets. Thistends to maximize the suspending liquid removal and to reduce thepossibility of forming Siamese twin aggregates. This movement may be ofessentially two types: (1) movement with respect to the path of slurrydrop whichentails little or no mixing of the particles; and (2) mixingof the particles.

The movement of the particle bed without mixing of the particles in' thebed is conveniently accomplished by placingv the solid of the particlebed on a conveyor belt and moving the belt in an essentiallyperpendicular plane to the path of the slurry droplet. This moves freshsolid of the particle bed continuously into the droplet target areawhile little or no mixing of the solid in the particle bed isexperienced. An alternative to moving the bed is moving the source ofthe droplets in such a manner that the droplets fall on fresh solid ofthe particle bed. Either of. these techniques can be beneficiallyapplied to the preparation of amphora.

The second method of imparting movement to the particle bed is a mixingof the solid within the bed. This movement is conveniently accomplishedby agitation, flufling, fluidization, stirring, mixing, blending orcontinuous removal and make-up of particles in the dropping zone. Suchmovement is normally conducted during and after droplets are droppedinto the particle bed. This movement does not have a desirable effect onthe preparation of amphora.

As a unified process, the slurry, particle bed and drop conditions arechosen to give thedesired rate of rigidification.'One important variablein the conditions is the temperature. Although the slurry drop canbejconducted at any temperature, the rate of rigidification is generallyincreased as the temperature is increased. As discussed in relation tothe suspending liquid and particle bed, the rate of rigidification wouldalso increase with the increasing vapor pressure of thesuspending'liquid and the increasing porosity of the solid in theparticle bed.

In the process of the invention, the discrete particles of solid in thedroplets of slurry are agglomerated ,to form an aggregate. Theseaggregates as they are formed may, in some cases, have a thin coating ofthe solid which forms the particle bed. This coating. in most cases iseasily removed by agitation, such as mild vibration of the aggregates ona screen. In cases where a more adherent coating is formed, othertechniques of solid .re-

moval can be conveniently applied.

The nature of the aggregates formed in the present invention varysubstantially as the components of the slurry are altered. It ispossible, however, to produce very coherent, attrition-resistantaggregates by the process of the invention. These aggregates areespecially useful in fixed-bed catalytic reactors because of theirspherical 'shape and stability.

8 using amphora techniques. These aggregates with a void center areespecially desirable for catalysts becausethe exposed surface issubstantially increased as compared to normal tablets, and problems ofdiffusion of reactants and products through the catalyst aresignificantly reduced. Although the exact mechanism by which theseamphora are made is not known, they can be produced by a relativelysimple process. In this preparation, the droplets of a slurry having aviscosity in the lower half of our preferred range are formed anddropped onto a static powder bed in such manner that the total dropletis not immersed in the powder. Without agitation, the droplet is allowedto dry in the particle bed. Surprisingly, the predominant product formedis a rounded aggregate having a single cavity in the externalsurfacecommunicating toa void center. Also produced in this process are someaggregates that have a void center and no communicating cavity from theexternal surface.

Whether amphora or other aggregates are prepared b use of the presentinvention, the invention provides a .very suitable technique foragglomerating distinct particles into a cohesive aggregate without theuse of compaction techniques.

DESCRIPTION OF THE DRAWING FIG. 1 shows a half-section view of a typicalamphora which is an aggregate having a single cavity in the externalsurface communicating to a void center. These amphora can bemanufactured by the process of the present invention and vary widely inshape and size according to the process employed.

FIG. 2 shows an apparatus which can be used to manufacture theaggregates of the invention. Referring to FIG. 2, there is a powder feedreservoir 1, a slurry feed' reservoir 2, equipped with a stirrer 3, adryer 4, moving belt 5 which is an an essentially solid belt, movingscreen 6 which is such a mesh screen so that the'ag gregates areretained on the screen while the powder falls through the screen, powderhopper 7 and aggregate hopper 8. p

In the operation of the apparatus, aquantity of small particles of thesolid into which the slurry is to be dropped is placed into the powderfeed reservoir. By gravity action, this powder is fed onto mixing belt5. The powder is evenly distributed over the belt by leveling edge 9 insuch a manner that a level, substantially-uniform powder bed 10 isobtained on moving belt 5. I r

The slurry feed reservoir 2 is charged with the slurry to be dropped.The suspension of the particles in the slurry as discrete entities ismaintained by stirring from stirrer 3. The slurry is fed through aplurality of droplet outlets 11 where distinct droplets of slurry areformed and allowed to drop by gravity onto the powder bed, 10. Thedroplets are dropped from a height such that the droplets are nottotally immersed in the powder bed 10.

The droplets in the powder bed 10 are transferred by the movement ofmoving belt 5 to a drying zone where- 'in the droplets are dried bydryer 4. The temperature and conditions of this drying zone may varywidely'and are dependent upon the desired nature of the final aggregate.

From the drying zone, the dried aggregates are then transferred inpowder bed 10 by means of moving belt 5 to a moving screen 6. Thespacing of the screen is such that the powder, into which the dropletsare dropped, readily falls through the screen and is caught'in powdercollector 7. From powder collector 7 the powder is conveniently recycledto the powder feed ,1. During the recycle, not shown, the. powder couldbe regenerated for use by some appropriate technique, such as drying.

' The moving screen 6 has a spacing such that the aggregates produced bythe technique of the present invention do not pass through the'scre'en..Thus, a separation of the powder and aggregates of theinvention is effected. Theaggregates produced are then transferred tothe aggregate collector 8 where the aggregates are collected and storedfor further use. If necessary, moving screen 6 can optionally bevibrated to agitate the aggregates in such a manner that essentially allpowder from powder bed 10 is removed from the aggregate.

SPECIFIC EMBODIMENTS Examples 1-14.Preparation of aggregates usingvarious techniques Aggregates of the invention were prepared by mixing10 parts of a uncalcined catalytic metal oxide having the empericalformula K Ni Co 5Fe BiP Mo -,O and 3 parts of silica added as a 40%ammonia stabilized silica sol. When the mixture was homogeneous, it wasallowed to gel and stand for 20 hours. The hydrogel formed plus a smallamount of water were mixed together in the blender. As the time spent inthe blender increased, the viscosity of the gel decreased. Samples weretaken at various time intervals and used in the process of theinvention. The viscosity of the samples can be maintained by loweringthe pH of the mixture.

Samples of the slurry were dispersed through a medicine dropper. Theparticle bed contained a solid of essen tially the samecomposition asthe-solid suspended inthe slurry. The particle size was a rather randomdistribution of particles in the range cited in Table I-. The particlebed was a static bed maintained at room temperature, the drop height,viscosity of the slurry, particle size of the bed and description of theaggregate formed are shown in Table I. All aggregates formed wereapproximately 4 mm. in diameter.

In the process, the slurry was dropped from the medicine dropper ontothe static bed and allowed to rest on they surface of the static bed fora few minutes; The particle bed was then shaken to completely cover thepartiallyhardened slurry droplet, and the aggregate was allowed to dryfor a few minutes. The aggregates were retrieved from the particle bedand dried in an oven. Any surface dust on the aggregate was then removedby a slight vibration of the oven-dried aggregate. The descriptions ofthese aggregates are shown in Table I. Spherical describes thoseexperiments where the product obtained was visually observed to containa predominance of substantially spherical aggregates. Semisphericaldescribes those experiments where the product obtained was visuallyobserved to contain a predominance of distorted spherical aggregates.All aggregates formed were very attrition resistant.

TABLE I [Aggregates prepared using various techniques] Drop Particleheight, Viscossize of Example inches ity, cp. bed, a Description ofaggregate l. 520 149 Semispherical amphora. 520 l49 Semiflat amphora.

1 1,140 149 Semispheneal amphora. 1 2,100 149 Do. 1 2,100 44Spherical'dimpled. 1 4,580 149 Spherical. 1 6,370 149 D0. 1 10,300 149D0. 1 680 44 Spherical amphora. 1 680 l49 Semispherical amphora. 1 68088 149 Do. 1 680 44 Spherical dimplcd bed temperature 100 C. 2 680 l49Less spherical than Ex. 9. 4 680 149 Flatter than 12, larger opening inamphora.

-20.Preparation of composition Examples aggregates of various ing theslurries with the components shown in Table II, adding enough water toobtain a viscosity of roughly 3000 centipoise by visual observations,and dropping the slurry at a drop height of about 1 inch into a staticbed of a fluorocarbon support sold under the trade name Fluoropak by theFluorocarbon Company. The aggregates formed in these experiments aredescribed in Table II.

, TABLE II [Preparation of aggregates of various compositions]Description Example Slurry composition of aggregate 15 Aqueous emulsionof polybutadiene con- Spherical.

- taining 65% solids. 16 Aqueous emulsion of copolymer of acry- Do.

' lonitrile and methacrylic acid containing 29.9% solids. 17 6.5 g.cobalt molybdate on alumina, 6.5 g. D0.

40% silica sol. 18 3.5 g. cobalt molybdate on alumina, 3.5 g. Do.

dispersible alumina. 19-... 8.0 g.'0.5% Pd on molecular sieve, 3.5 g.Do.-

40% silica sol. 20 3.5 g. NiO on silica alumina, 3.0 g. 40% Do.

silica sol.

Examples 2130.-Preparation of aggregates using different particle bedsIn the same manner as shown by the examples above, a slurry was preparedusing equal parts by weight of pulverized 20% cobalt molybdate onalumina and dispersible alumina sold as Dispal M by Continental OilCompany. To these dry ingredients enough water was added to obtain aslurry having a viscosity of roughly 3000 centipoise by visualobservation of the consistency of the mixture. From a drop height ofabout 1 inch, this slurry was dropped into various particle beds of finemesh to determine the effect of the particle bed upon the aggregateformed. The aggregates were dried at C. The description of the driedaggregatesand the particle bedsare shown in Table III.

3O IL Glass microbeads, 60-80 mesh Semisphe Examples 31-46.Aggregatesprepared from various 'slurriesland various particle beds Using theprocedures described above, various slurries of different compositionwere dropped from a drop height of about 1 inch into various particlebeds. Unless specified, the slurries were prepared by mixing thesuspending liquid and solid until. a slurry of the desired consistency,roughly a viscosity of 3000 centipoise, was obtained. The composition ofthe slurries, the composition of the particle beds and the descriptionof the aggregate formed are found 11 in Table IV. Some of the aggregateswere observed to bear a coating of the solid from the particle bed.

TABLE IV [Aggregates prepared from various slurries and various particlebeds Ex. Slurry Particle bed Aggregate 31- Aq. urea Powdered pumice..-Spherical, amphora. 32.... Ag. NH4N03 Powdered NH4NO3 Spherical. 33. Aq.pulverized potato chips" Pulverized NaCl Do. 34- Aq. ground animalcrackers Powdered sugar. 35. Aq. ground corn flakes ..do 36 doPulverized corn flakes. 37- Aq. alumina gel Alumina, 80-200 mesh.

38. 10 g. alumina, 4 g. 11:0, 6.5 g. do Spherical,

40% silica sol. 39- 5 g. bismuth phosphomolyb- Powdered bismuth Do.

date, 2 g. 1120, 5.0 g. 40% phosphomolybdate. silica sol. 40- 5g. T102,3 g. H2O TiOz, 80-200 mesh Semispherical. 41-... 5g. T102, 1.5g. HzO,1g.40% do Do.

silica sol. 42. 1 g. active carbon, 1.25 g. glyo- Active carbon, 200Sphererine, 2.0 g. 20. mes 1. ieal. 43"-- 1 g. active carbon, 1.25 40%Active carbon, 200 Spherical.

silica sol, 2 g. H2O. mesh. 44- 1 g lactive carbon, 2 g. light do Do.

01 45. 25 g. urea, 3 g. (P1110280 1 g. Powdered bentonite Do.

NH4N03, 6 g. B20. clay. 46. Aq. (NHmS Fine beads of poly, Do.

styrene sold as Porapak:

' Easily broken in normal handling.

Examples 4752.Eficct of movement of the particle bed The slurry ofExample 1 having a viscosity of 3000 centipoise was pumped to amulti-orifice dropper. The droplets were dropped onto a particle bedhaving a solid of essentially the same composition as that of the solidin the slurry and having a particle size distribution less than 14911..The efiect of movement in the bed was observed in relation to the shapeof the aggregates formed. The conditions of these experiments andresults are given in Table V. The flufied bed was provided by rotatingthe particle bed on an inclined plane in such a manner that a fluifypowder was formed. This fluify powder was then allowed to remain staticfor the dropping. For the static bed, there as no attempt to flulf theparticle bed. For the fluid bed, a stream of air was passed through theparticle bed in such a manner that the volume of the bed was expanded to120% of the original volume when no air was passed through the bed. Theslow-moving bed was a static bed placed on a moving belt.

TABLE V [Efiect of movement in the particle bed] Additional bed move-Aggregate Percent Examples 53-67.Altering the properties of theaggregates by the addition of ingredients to the slurry In the samemanner as shown in Example 1, slurries were prepared and dropped into astatic bed. The slurries of these examples, however, are difierent inthat they contained various additives to cause alteration in theproperties of the aggregates formed. The additives were added to aslurry consisting of 750 g. of the mixed uncalcined metal oxides, 193 g.of 40% silica sol and 225 g. H O. After dropping, the aggregates wereair dried for 30 minutes at room temperature, dried at 120 C. for twohours and heated in air at 290 C. for one hour, 425 C. for one hour andcalcined at 620 C. The pore volume was calculated from'helium, mercurypycnometer measurements and the apparent bulk density. The effect of theadditives on the pore volume of the aggregates is shown as compared toExample 67 where nothing was added.

TAB LE VI [Effect of additives on aggregates] Pore Wt. volume, ExampleAdditive percent cc./g.

53 Graphite 5 O. 245 Carbon black l0 0. 430 55 Ethyl cellulose 0. 436Polyb 5 0. 288 do 20 0. 451 58 Copolymer of acrylonitrile and meth- 5 0.287

acrylic acid emulsion.

15 59...- Solid copolymer of Ex. 58 5 0. 309 60 10 0. 223 61--.. 100.458 62 10 0. 332 63 5 0. 327 64- 10 0. 420 65 35 0. 565 66 2 0. 250

0 67 None 0.222

Using the techniques of the invention discussed above, the presentinvention could be used to alleviate various problems of aggregation andcapitalize on opportunities such as those discussed below.

Iron oxide powder emanating from smelting operations is entrapped inwater to form a dense slurry. Coal far is added to the slurry as ahinder, the slurry is formed into droplets and the droplets arecontacted with a bed of small iron metal particles. Rounded aggregatesof iron oxide are formed which can be sold or recycled.

From an electrostatic trap on the flue of a coal-fired boiler, largeaccumulations of fly ash are removed. The lly ash is suspended in waterand molasses is added to the slurry as a binder and rounded aggregatesare prepared by contacting droplets of this slurry with a fluid bed ofcarbon particles.

An aqueous slurry of aspirin crystals, starch and a surfactant is formedinto droplets and dropped into a powdered fluifed bed of small aspirincrystals. A round aspirin aggregate is obtained.

Urea is slurried in chloroform, droplets are formed from the slurry andthe droplets are contacted with a moving powdered bed of small aluminaparticles.

Sodium hydroxide granules are slurried with water or acetone. The slurryis formed into large droplets, and the droplets are contacted with afluid bed of sodium hydroxide granules. Rounded agglomerates of sodiumhydroxide in diameter are formed. As a modification of the abovetechnique, a small amount of a surfactant is added to the sodiumhydroxide slurry to enhance the solubility of the final aggregateproduct.

Fine particles of a melamine resin are suspended in water and dropletsof the slurry are formed. The droplets of slurry are contacted with amoving bed of calcium carbonate and aggregates of melamine are formed.

A mixture containing equal parts of ammonium nitrate and ammoniumsulfate is slurried in ether and polyvinyl acetate is added as a binder.Droplets of the slurry are formed and contacted with small crystals ofammonium sulfate to form small attrition-resistant spheres of the slurrymixture.

We claim:

1. A process for preparing aggregates comprising (a) preparing a slurry,said slurry comprising a suspending liquid and distinct particles of afirst solid suspended in said liquid; (b) preparing a particle bedconsisting of particles of a second solid;

(c) forming droplets of said slurry; and

(d) dropping said droplets of said slurry into said particle bed underconditions Where said suspending liquid is at least partially removedfrom the slurry 13 droplet to form an aggregate of said distinctparticles of said first solid.

2. The process of Claim 1 wherein said suspending liquid is water.

3. The process of Claim 1 wherein the first solid is a catalyst or acatalyst precursor.

4. The process of Claim 1 wherein said first solid contains at leastbismuth and molybdenum.

5. The process of Claim 1 wherein the particle size of the first solidis less than about a millimeter.

6. The process of Claim 1 wherein the slurry has an apparent viscosityof about 400 to about 15,000 centipoise.

7. The process of Claim 1 wherein the particle bed is composed ofparticles having a size of below about 500 microns.

8. The process of Claim 1 wherein said first solid and said second solidare chemically similar.

9. The process of Claim 1 whereby an aggregate with a void center isproduced.

References Cited UNITED STATES PATENTS Murray et a1. 252448 Richardsonet al. 252448 Whiteley 252448 Kearby 252448 McKinley 117-6 Gidlow et a1.117--6 Loertscher et al. 117--6 Hudson 117-6 Vesely 252448 Netherlands.

MICHAEL SOFOCLEOUS, Primary Examiner U.S. Cl. X.R.

1. A PROCESS FOR PREPARING AGGREGATES COMPRISING 8A) PREPARING A SLURRY,SAID SLURRY COMPRISING A SUSPENDING LIQUID AND DISTINCT PARTICLES OF AFIRST SOLID SUSPENDED IN SAID LIQUID, (B) PREPARING A PARTICLE BEDCONSISTING OF PARTICLES OF A SECOND SOLID, (C) FORMING DROPLETS OF SAIDSLURRY, AND (D) DROPPING SAID DROPLETS OF SAID SLURRY INTO SAID PARTICLEBED UNDER CONDITIONS WHERE SAID SUSPENDING LIQUID IS AT LAST PARTIALLYREMOVED FROM THE SLURRY DROPLET TO FORM AN AGGREGATE OF SAID DISTINCTPARTICLES OF SAID FIRST SOLID.